1. Field of the Invention
This invention relates to magnetic recording mediums such as magnetic tapes, floppy disks, hard disks and allied articles and more particularly, to magnetic recording mediums particularly suitable for use in magnetic disk apparatus such as computers.
2. Description of the Prior Art
Magnetic recording mediums which are used in information recording and reproducing apparatus such as, for example, magnetic disk apparatus, are of the type obtained by applying a magnetic paint of magnetic powder, dispersed in a solvent dissolving suitable resin binders, onto a non-magnetic substrate, and baking and curing the applied paint.
As information recording and reproducing apparatus are now becoming high in performance, there is an increasing demand for magnetic recording mediums of higher density. In order to meet the demand, there have been proposed a number of magnetic recording mediums including, for example, a medium whose magnetic recording layer has a smaller thickness than was used for ordinary purposes, a medium having a magnetic recording layer which is made of a completely uniform dispersion of magnetic powder, and magnetic recording mediums using magnetic powders having high coercive force, such as magnetic Co-modified gamma-Fe.sub.2 O.sub.3 powder, magnetic Cr.sub.2 O.sub.3 powder, and magnetic metallic powders.
When the magnetic recording layer is made thin, the amount of magnetic powder is also reduced. It is important not to reduce the amount of magnetic powder, but to reduce the amount of other ingredients such as, for example, a binder. If, however, the amount of a binder is reduced, necessary properties of the magnetic recording medium, e.g. durability, will be sacrificed.
On the other hand, magnetic powders with high coercive force are usually available as small-size particles and have a large acicular ratio, so that they have a large specific surface area. This is disadvantageous in that such powders are less likely to disperse than conventional gamma-Fe.sub.2 O.sub.3 powder. It undesirably takes a longer time before the magnetic powders are dispersed to obtain uniform magnetic paints. The long dispersion operation results in a lowering of coercive force due to the breakage of the magnetic powder.